From 74ae08376b6f390fdcdb7239b3cd8650b440252f Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Wed, 8 Nov 2023 21:30:29 -0800 Subject: [PATCH] selftests/bpf: Fix pyperf180 compilation failure with llvm18 With latest llvm18 (main branch of llvm-project repo), when building bpf selftests, [~/work/bpf-next (master)]$ make -C tools/testing/selftests/bpf LLVM=1 -j The following compilation error happens: fatal error: error in backend: Branch target out of insn range ... Stack dump: 0. Program arguments: clang -g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf -I/home/yhs/work/bpf-next/tools/include/uapi -I/home/yhs/work/bpf-next/tools/testing/selftests/usr/include -idirafter /home/yhs/work/llvm-project/llvm/build.18/install/lib/clang/18/include -idirafter /usr/local/include -idirafter /usr/include -Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 --target=bpf -c progs/pyperf180.c -mcpu=v3 -o /home/yhs/work/bpf-next/tools/testing/selftests/bpf/pyperf180.bpf.o 1. parser at end of file 2. Code generation ... The compilation failure only happens to cpu=v2 and cpu=v3. cpu=v4 is okay since cpu=v4 supports 32-bit branch target offset. The above failure is due to upstream llvm patch [1] where some inlining behavior are changed in llvm18. To workaround the issue, previously all 180 loop iterations are fully unrolled. Now, the fully unrolling count is changed to 90 for llvm18 and later. This reduced some otherwise long branch target distance, and fixed the compilation failure. [1] https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e Signed-off-by: Yonghong Song Tested-by: Eduard Zingerman --- tools/testing/selftests/bpf/progs/pyperf180.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/pyperf180.c b/tools/testing/selftests/bpf/progs/pyperf180.c index c39f559d3100e..3c38f3e128360 100644 --- a/tools/testing/selftests/bpf/progs/pyperf180.c +++ b/tools/testing/selftests/bpf/progs/pyperf180.c @@ -1,4 +1,17 @@ // SPDX-License-Identifier: GPL-2.0 // Copyright (c) 2019 Facebook #define STACK_MAX_LEN 180 + +/* llvm upstream commit at llvm18 + * https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e + * changed inlining behavior and caused compilation failure as some branch + * target distance exceeded 16bit representation which is the maximum for + * cpu v1/v2/v3. To workaround this, for llvm18 and later, let us set unroll_count + * to be 90, which reduced some branch target distances and resolved the + * compilation failure. + */ +#if __clang_major__ >= 18 +#define UNROLL_COUNT 90 +#endif + #include "pyperf.h"